Ionic compounds are compounds composed of ions, which are atoms or molecules that have lost or gained electrons, resulting in a net electric charge. The electrostatic attraction between the oppositely charged ions holds the compound together.

Of the four compounds you listed, only TiO$_2$ is an ionic compound. It consists of positively charged titanium ions (Ti$^{4+}$) and negatively charged oxide ions (O$^{2-}$). The strong electrostatic attraction between the titanium and oxide ions forms the stable ionic compound TiO$_2$.

On the other hand, SO$_2$, ClO$_2$, and H$_2$O$_2$ are molecular compounds, not ionic compounds. In these compounds, atoms are covalently bonded, sharing electrons to achieve a stable electron configuration. There is no transfer of electrons or formation of ions in these cases.

Here's a summary of the compounds:

- TiO$_2$: Ionic compound (titanium dioxide)

- SO$_2$: Molecular compound (sulfur dioxide)

- ClO$_2$: Molecular compound (chlorine dioxide)

- H$_2$O$_2$: Molecular compound (hydrogen peroxide)